Purpose: Soft skills are essential not only for students but also for employees in any workplace. Some factors influence the development of soft skills in high schools. This study investigates the effect of psychological capital (PsyCap) on soft skills through the role of psychological well-being at different students' grade levels. Design/methodology/approach: Three scales (i.e. the Psychological Capital Questionnaire, the Scale of Psychological Well-being and the soft skills assessment) were used on 707 high school students from seven senior high schools. The data were analysed using a moderated-mediation regression technique to reveal the conditional indirect effect of PsyCap on soft skills. Findings: The results suggested that students' grade levels moderated the indirect effect of PsyCap on soft skills via psychological well-being. Students in higher grades showed a stronger impact of PsyCap on soft skills via psychological well-being. Research limitations/implications: The psychological states of students should be regarded as one of the most critical aspects of education and career advancement. Schools should assist students in developing their soft skills. Students, regardless of grade level, would begin to occupy their PsyCap, ensure their psychological well-being and finally, engage in soft skills development activities. Originality/value: This current study has shifted from simply assessing soft skills to investigating some avenues for developing soft skills in various contexts and areas. If the theoretical model is well established, teachers and educators can effectively improve soft skills intervention by understanding the antecedents of soft skills.